Edit in JSFiddle

var $foo = $('#foo1');
console.log('Index: ' + $foo.index()); // 1

var $listItem = $('li');
// this implicitly calls .last()
console.log('Index: ' + $listItem.index()); // 3
console.log('Index: ' + $listItem.last().index()); // 3

var $div = $('div');

// this implicitly calls .last()
console.log('Index: ' + $div.index());  // 4
console.log('Index: ' + $div.last().index()); // 4